This invention relates to food preparation ovens and in particular to a food preparation oven for preparing pizza and similar food products. Specifically the invention relates to an oven for preparing food products such as pizza by means of air impingement and steam impingement.
In the fast food restaurant business, the speed with which food products can be prepared is extremely important. Due to the ever increasing competitiveness of the fast food business, restaurants need to be able to serve diners ever more quickly so that the food preparation time must be reduced. Restaurants will, therefore, be able to handle more people without adding additional space and seating areas. The need to reduce food preparation time is especially important for foods such as pizza and the like as the preparation time for pizza has normally been longer than for competing fast food products such as hamburgers, chicken, and the like.
One of the reasons that preparation time for pizzas is longer than for other fast foods is the nature of the pizza product. As opposed to other types of fast foods which primarily consist of meat products such as beef, chicken, or fish, all of which can be prepared rather quickly by grill frying or deep fat frying, pizza consists of a combination of a dough shell and a variety of toppings such as various types of cheese, meats, and vegetables such as onions, mushrooms, green peppers and the like, all of which must be adequately cooked rather than deep fried and which, therefore, require special handling. It is therefore more difficult to cook a pizza and similar food products very quickly as opposed to preparing items such as hot dogs, hamburgers, fried chicken, and the like.
To increase the speed at which pizzas are prepared, it is not sufficient to merely increase the temperature of the oven in which the pizza is cooked. An increase in temperature could result in breakdown of the components of the pizza, and could possibly result in burning the pizza.
Advances have been made in the speed at which pizzas may be prepared by improvements in prior art oven structures. Thus, in the preparation of pizzas with conventional ovens, the time for preparing a pizza was approximately 16-18 minutes from the time the pizza entered the oven to the time the pizza left the oven. Impingement ovens, such as disclosed in U.S. Pat. No. 4,462,383, which is assigned to the assignee of record of the instant application, have reduced the preparation time for pizza to approximately 8 minutes. However, it is desired to reduce the preparation time even further while retaining a high quality pizza product.
Several prior art solutions have been suggested for reducing the preparation time of pizzas and the like. These solutions have sought to decrease the preparation time of pizzas by increasing the amount of heat energy transferred to the pizza product without causing deleterious effects on the taste, texture, and appearance of the finished food product. Thus, for instance, various types of baking pans have been proposed whereby more heat energy could be supplied to a food product in a given amount of time. Additionally, it has been suggested to control the rates of heat energy impinging upon the bottom surface of a food product versus the top surface of a food product. Such an approach is disclosed in U.S. Pat. No. 4,154,861, wherein it is suggested that a greater amount of heat can be transferred to the bottom of a pizza product than to the top of a pizza product. However, applicant has found that the amount of heat energy which can be transferred to the pizza product and the like by this method is limited and that the desired reduction in preparation time for such products can, therefore, not be achieved in this manner.
Pizzas are commonly prepared with a dough shell to which is added a layer of sauce, cheese, meats and vegetables. This mass, when added to the pizza, makes heat transfer to the center of the pizza extremely difficult. If it is attempted to transfer a large amount of heat energy through the various toppings by impingement with hot air jets, the toppings will tend to burn. Thus, conventionally, most of the heat energy has been supplied to pizzas through the bottom surface. However, it has also been found that if a maximum amount of heat energy is rapidly supplied to the bottom dough layer of the pizza while the pizza is still relatively uncooked, the dough will bake rapidly and form air pockets therein, thereby forming an insulator and preventing the rapid addition of further heat energy through the cooked dough. Thus it is desired to provide an oven wherein heat energy may be rapidly supplied to both the top and bottom surfaces of a pizza and wherein the heat energy input is controlled such that the supply of heat energy to both the top and bottom surfaces of the pizza is maximized without cooking the pizza dough too rapidly.
Another problem with rapidly adding heat energy to the pizza by means of conventional air impingement is that it may cause the outer layers of the pizza toppings to dry out, thereby resulting in unacceptable appearance, texture, and flavor of the pizza. In some prior art pizza ovens, it has been suggested to spray moisture into the hot air supply for the air impingement jets. The added moisture helps prevent drying out of the top surface of the pizza. However, a disadvantage of adding moisture to the hot air stream is that the water absorbs heat energy from the hot air and thereby cools the air. What is therefore desired is to provide an oven wherein high heat energy may be transferred to a pizza product for a reduction in cooking time while achieving acceptable quality of the cooked pizza product.
It has been proposed in the prior art ovens to use steam for preparing food products such as meat. The use of steam is advantageous because of the large amount of heat energy which is released when the steam gives up its latent heat of vaporization. Steam is therefore an efficient heat transfer medium. However, due to the effect of steam on the appearance of food, it has been suggested to use both steam and infrared heat whereby the meat products are cooked rapidly by the steam and are broiled by the infrared energy to give an acceptable texture and appearance to the meat products. One example of an oven incorporating steam and infrared energy is disclosed in U.S. Pat. No. 3,736,860, wherein a conveyor is used to move food products contained in open shallow pans through an oven and wherein steam is sprayed from a plurality of spray tubes both onto the top surface of the food products and onto the bottoms of the pans wherein the food is contained. The disadvantage of this method is that the steam will not be very effective in transferring heat to the food through the bottom of the pan unless the steam is superheated to a high degree. However, if the steam is superheated to a high degree, the steam, which is sprayed onto the top surface of the food product, may cause the food to have an unacceptable appearance and to be overcooked or possibly to burn. Furthermore, to generate highly superheated steam requires complicated steam generating equipment which is undesirable in the oven environment.
It has also been suggested to cook food products by means of both steam and hot air convection. However, convection processes are not nearly as efficient in transferring heat to a food product as are impingement processes and therefore convection and steam processes are not sufficiently effective in reducing the time necessary to cook food products.
It is therefore desired to provide a food preparation apparatus for cooking pizzas wherein a very efficient heat transfer mechanism is used. It is furthermore desired to provide such an apparatus wherein the heat transfer process is designed in such a way to eliminate the above-identified problems in the preparation of pizza and similar food products. It is also desired to provide a food preparation apparatus wherein the sequencing of heat energy transfer to the food product is arranged for maximum cook time reduction. Lastly, it is desired to provide a food preparation apparatus wherein a pizza product or the like is provided which is cooked in a minimum amount of time and which is of high quality in appearance, texture, and flavor.